Prior television sensors tend to only resolve either bright objects, by attenuation of the light, and thereby obscure dimly illuminated detail, or to allow bright scene areas to saturate the detector in order to observe dimly lit detail. The disadvantage of a system having a single sensor tube is that there is a finite dynamic range of brightness values which can be faithfully sensed by the device. Thus in high dynamic range scenes, details of a scene may be lost due to a conventional television camera's lack of intra-scene range. The National Aeronautics and Space Administration has a need for a camera system capable of handling such high dynamic range scenes, particularly for use on spacecraft in an orbital environment. There, it may be necessary to use television sensors which can handle scenes having very bright areas as well as very dimly lighted background areas which must not be attenuated.
One prior art sensing device having to do with the intensities of illuminated scenes is U.S. Pat. No. 4.124,278 to Grinberg et al. This patent discloses the concept of employing birefringent devices, such as liquid crystal light valves, for generating the subtraction of images; however, this reference does not accomplish the object of the present invention, namely, to selectively attenuate bright areas of a viewed scene so as to make the scene fit within the dynamic range of a sensing system.
U.S. Pat. No. 4,032,954 to Grinberg et al discloses the broad concept of a photo-activated alternating current liquid crystal light valve which can impose an AC voltage on a liquid crystal layer in direct relationship, both spatially and temporally, to the variations of intensity of an incident input image; however, this reference does not contemplate or disclose anything relating to the concept of combining the liquid crystal light valve with a wide dynamic range video camera and selectively attenuating independent areas of a scene in order to fit bright objects within the dynamic range of the system.
A third prior art patent. U.S. Pat. No. 4,227,201 to Grinberg et al discloses interface means for coupling CCD signals to a liquid crystal; however, this reference does not disclose or contemplate the use in combination of a wide dynamic range video camera employing a liquid crystal light valve to selectively attenuate areas of a viewed scene.
Thus the object of this invention is to go beyond the teachings of the prior art, particularly the Grinberg et al patents mentioned above, and produce a television camera sensing device which will selectively attenuate bright objects to fit within the sensor's dynamic range while dim images within the viewing scene are not attenuated.